There have been various approaches to treatment of municipal refuse. In view of the fact that using refuse as landfill or incineration of refuse causes secondary problems, recent practical methods of municipal refuse treatment have been to reduce the volume of refuse or to treat the refuse for reuse as a resource. Particularly, the method of sorting municipal refuse for reuse has become more and more prevailing. Kitchen refuse which has been sorted out by the sorting method or kitchen refuse collected initially as such can be effectively converted into compost. Obviously the treatment capacity of a composting apparatus per unit area required for installing the apparatus can be made higher by increasing the height of the pile of the material. In practical operation, however, when the pile of the material is too high the material packs down into a mass in which air permeability is reduced, thereby retarding aerobic fermentation therein. This tendency is significant in material having a relatively high water content, such as kitchen refuse, organic sludge, and the like. The known multistage vertical cylindrical composting apparatus comprising a plurality of horizontal floors in which material is allowed to fall successively to the floor below can reduce the thickness of the layer of composting material on each floor relative to the single-stage composting apparatus and can, accordingly, eliminate some of the disadvantages mentioned above and increase the treatment capacity of the apparatus.
However, the conventional multistage vertical cylindrical composting apparatus, in which the material is moved by a rake rotating about a cylindrical shaft in conjunction with some agitation, has disadvantages in that substantial agitation of the material is not performed and a relatively large amount of power is required to rotate the rake of having a large radius while shearing the material between the rake and the floor. Another disadvantage of the material raking operation on the floor is that it tends to consolidate the material into dense masses resulting in insufficient agitation particularly in material of high water content, thereby retarding fermentation of the material. Consequently, in the conventional composting apparatus it is impossible to increase the thickness of the material in each stage and to expect a satisfactory agitation effect provided by the rake.